Plant and method for purifying an isomeric monomer

Patent metadata

Field	Value
Publication number	US-11613518-B2
Application number	US-201816771367-A
Country	US
Kind code	B2
Filing date	Nov 26, 2018
Priority date	Dec 14, 2017
Publication date	Mar 28, 2023
Grant date	Mar 28, 2023

Abstract

A plant for preparing a purified isomeric methylene diphenyl diisocyanate monomer from a mixture of different isomeric monomers is disclosed herein. The plant can comprise a distillation apparatus, which comprises: a) a distillation column including a structured packing, b) a source for a mixture of different isomeric methylene diphenyl diisocyanate monomers, c) an evaporator, d) an overhead vapor condenser, e) optionally, an overhead vacuum system and f) a flow-controlled reflux system. The overhead vapor condenser comprises a shell and tube arrangement and is embodied so as to directly subcool the condensate to less than 47° C. The flow-controlled reflux system comprises a heater, which is embodied so as to reheat a partial stream of the condensate formed in the overhead vapor condenser up to 190° C.

First claim

The invention claimed is:

1. A plant for preparing a purified isomeric monomer from a mixture of different isomeric methylene diphenyl diisocyanate monomers, wherein the plant comprises a distillation apparatus, which comprises:
a) a distillation column including a structured packing,
b) a source for a mixture of different isomeric methylene diphenyl diisocyanate monomers,
c) an evaporator,
d) an overhead vapor condenser,
e) an overhead vacuum system and
f) a flow-controlled reflux system,
wherein the source is connected with the evaporator, the evaporator is connected with a lower part of the distillation column via a line, the distillation column leads to the evaporator via another line, and a head of the distillation column leads into the overhead vapor condenser,
wherein the overhead vapor condenser is connected to the flow-controlled reflux system and comprises a shell and tube arrangement configured to directly subcool condensate to less than 47° C., and the overhead vapor condenser is provided with a vapor outlet line, which is in fluid connection with the overhead vacuum system, which in turn is provided via a line in fluid connection with an inlet at an upper part of the distillation column, and
wherein the flow-controlled reflux system comprises a heater configured to reheat a partial stream of the condensate formed in the overhead vapor condenser up to 190° C.

2. The plant in accordance with claim 1 , wherein the plant does not comprise any further distillation column.

3. The plant in accordance with claim 1 , wherein the plant further comprises, downstream of the distillation apparatus, a falling-film crystallization apparatus or a suspension crystallization apparatus, wherein the overhead vapor condenser is provided with a withdrawal line, wherein the falling-film crystallization apparatus or suspension crystallization apparatus is connected with the withdrawal line.

4. The plant in accordance with claim 1 , wherein the source for the mixture of different isomeric monomers comprises different isomers of methylene diphenyl diisocyanate, which comprise 4,4′-methylene diphenyl diisocyanate and at least one of 2,2′-methylene diphenyl diisocyanate, 2,4′-methylene diphenyl diisocyanate, as well as dimers, oligomers and polymers thereof.

5. The plant in accordance with claim 1 , wherein the overhead vapor condenser is configured to directly subcool the condensate to less than 46° C.

6. The plant in accordance with claim 1 , wherein the evaporator is a falling film evaporator or a thin film evaporator.

7. A process for preparing a purified methylene diphenyl diisocyanate from a crude mixture including different isomeric methylene diphenyl diisocyanate monomers as well as dimers, oligomers and polymers thereof, wherein the process is performed in a plant in accordance with claim 1 , wherein
(i) the mixture of different isomeric methylene diphenyl diisocyanate monomers is fed from the source into the evaporator, where liquid is evaporated;
(ii) generated vapor flows into the lower part of the distillation column; and
(iii) vapor is withdrawn from the head of the distillation column and transported into the overhead vapor condenser, in which the condensate is directly subcooled to less than 47° C., wherein remaining vapor is withdrawn from the overhead vapor condenser, led through the overhead vacuum system and returned into the upper part of the distillation column, a portion of the condensate is returned via the flow-controlled reflux system into the distillation column and another portion of the condensate is withdrawn as purified isomeric monomer.

8. The process in accordance with claim 7 , wherein the process is for preparing 4,4′-methylene diphenyl diisocyanate from a crude methylene diphenyl diisocyanate mixture including different isomers, dimers, oligomers and polymers of methylene diphenyl diisocyanate, wherein the mixture contains 4,4′-methylene diphenyl diisocyanate and at least one of 2,2′-methylene diphenyl diisocyanate, 2,4′-methylene diphenyl diisocyanate and oligomers thereof.

9. The process in accordance with claim 7 , wherein the pressure at the top of the distillation column is set to 2 to 10 mbar.

10. The process in accordance with claim 7 , wherein an average residence time of liquid in tubes of the overhead vapor condenser is adjusted to 30 seconds to 5 min.

11. The process in accordance with claim 7 , wherein the process is performed so that condensed liquid withdrawn from the overhead vapor condenser has a dimer content of less than 200 ppm.

12. The process in accordance with claim 7 , wherein the condensate withdrawn from the overhead vapor condenser has the following characteristics:
i) a dimer content of less than 200 ppm,
ii) a content of polymeric methylene diphenyl diisocyanate of at most 2000 ppm,
iii) a color of at most 100 APHA,
iv) a hydrolyzable chloride content of 10 to 150 ppm, and
v) a content of 4,4′-methylene diphenyl diisocyanate of 88 to 96% by weight,
wherein all of the criteria i) to v) are fulfilled.

13. The process in accordance with claim 7 , wherein condensed liquid withdrawn from the overhead vapor condenser is subsequently fed as liquid feed into a falling-film crystallization apparatus or a suspension crystallization apparatus.

Assignees

• Sulzer Management Ag

Inventors

• Faessler Peter
• Stepanski Manfred
• Jansen Halbe

Classifications

• C07C263/20 Primary

  Separation; Purification · CPC title

• C07C265/14 Primary

  containing at least two isocyanate groups bound to the same carbon skeleton · CPC title

• B01D5/009

  Collecting, removing and/or treatment of the condensate · CPC title

• B01D5/006

  with evaporation or distillation · CPC title

• B01D1/22

  by bringing a thin layer of the liquid into contact with a heated surface {(B01D1/065 takes precedence)} · CPC title